1. Field of the Invention
The present invention relates to technology for adjusting the gamma curve used in gamma correction.
2. Description of the Related Art
In image display devices such as projectors or liquid crystal displays, it sometimes occurs that an image which is actually displayed has lightness characteristics different from those of the input image, due to specific input/output characteristics of the device. In such image display devices, a so-called gamma curve indicating the relationship of input tone values to output tone values is pre-established in consideration of the input/output characteristics of the device, and gamma correction is performed through conversion of tone values of an input image in accordance with this gamma curve, so that the displayed image has lightness characteristics substantially identical to those of the input image.
There is sometimes a need to display such a gamma-corrected image as an image imparted with desired lightness characteristics with reference to considerations such as image content, for example, where it is desired to display an image that is lighter overall. Consequently, there have been proposed to date various image display devices that permit adjustment of the gamma curve, making it possible to display images having desired lightness characteristics.
There has also been proposed a gamma curve adjustment method which involves pre-establishing on the gamma curve a number of adjustment points corresponding to prescribed input tone values, and modifying the output tone values at these adjustment points to adjust the gamma curve (see JP2003-60914A, for example).
In the gamma curve adjustment method described in JP2003-60914A, consider the case where the plurality of adjustment points have been established as equidistant points with respect to input tone values, for example, as points at which input tone values in 10 bit tone data are 0, 128, 256, 384, 512, 768, 896, and 1023, respectively.
In this case, even if, for the purpose of deriving a gamma curve suitable for a relative dark image such as a movie, it were attempted to boost output tone values at relatively large number of points in the low tone range (the darker range), e.g. points at which input values are 10, 30, 60, 90, since adjustment points are not present at these points, a resultant problem is that the gamma curve cannot be adjusted to as to produce the desired gamma curve.
In the high tone range, on the other hand, despite the fact that it is sufficient to adjust a relatively small number of points, e.g. the two points at which input values are 768 and 1023, it is necessary to also adjust the adjustment point at which the input value is 896, a resultant problem is that gamma curve adjustment is time consuming.
Also, consider the case where, in the user interface for adjusting the gamma curve, the unit amount for increasing or decreasing output tone values (the minimum increment/decrement unit or the minimum/increment/decrement step) when specifying output tone values for adjustment points is set to a relatively small value, e.g. ±2 (tones), at all of the adjustment points.
In this case, if it is desired to specify an increase of an output tone value from 0 to 50 at the adjustment point at which the input tone value is 0 for example, it will be necessary to increase the output tone value 25 times (50÷2), and a resultant problem is that gamma curve adjustment is very time consuming.
Consider the case where, conversely, the aforementioned minimum increment/decrement unit is set to a relatively small value, e.g. ±4 (tones), at all of the adjustment points. In this case, as in the preceding case, if it is desired to specify an increase of an output tone value from 0 to 50 at the adjustment point at which the input tone value is 0 for example, since output tone value increases in increments of four tones, either 48 or 52 must be specified as the output tone value. A resultant problem is that the gamma curve cannot be adjusted in such a way as to produce the desired gamma curve.